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Mom and Dad Are Fighting in Your Genes--and in Your Brain
Discover, December 2008

Sometimes the best way to learn how the brain works is to watch what happens when it goes awry. When one part--a clump of neurons or a brain-building gene--doesn’t do what it is supposed to, the brain may fail in an illuminating way. Its failure may even expose some of the hidden foundations of the mind.

Neuroscientists have recently become fascinated with a particularly telling pair of rare brain disorders. One was identified in 1965 by English physician Harry Angelman, who was struck by the faces of three children he treated. These children were always smiling and often laughing. This disorder, now known as Angelman syndrome, affects around 1 in 20,000 children. Along with the smiles and laughs come other symptoms, some of which overlap those of severe autism. Many children with Angelman syndrome never learn to speak or read. They also keep their bodies in motion, often flapping their hands. When they nurse they suckle desperately, thrusting out their tongue.

Another similarly rare condition, called Prader-Willi syndrome, produces a different set of symptoms. Babies with Prader-Willi nurse very little--so little that they often have to be tube fed. However, once Prader-Willi children get to be a few years old, they develop an insatiable appetite. They will try to get around any obstacle put between them and food. Their fierce hunger is driven by a malfunctioning hypothalamus, a region deep in the brain that governs hunger and growth. Instead of autism, many people with Prader-Willi syndrome develop schizophrenia by adulthood, hearing voices and generating paranoid delusions.

Despite their differences, Prader-Willi and Angelman are two sides of the same coin. Scientists have searched for the genetic basis of the two syndromes and have tracked most cases of both to defects on the same spot of the human genome, a stretch of DNA on chromosome 15. Which disease a child gets depends on which parent’s chromosome 15 carries the defect (every person’s cells contain two genetic copies, one from the mother and one from the father). Prader-Willi syndrome is caused by a mutation in a father’s genes that deletes a chunk of DNA on chromosome 15. Angelman syndrome is associated with a mutation on the mother’s chromosome 15.

If you think back to the genetics you learned in school, this pattern makes no sense.

Now: The Rest of the Genome
The New York Times, November 11, 2008

Winner of the New York Times Publisher’s Award

Over the summer, Sonja Prohaska decided to try an experiment. She would spend a day without ever saying the word “gene.” Dr. Prohaska is a bioinformatician at the University of Leipzig in Germany. In other words, she spends most of her time gathering, organizing and analyzing information about genes. “It was like having someone tie your hand behind your back,” she said.

But Dr. Prohaska decided this awkward experiment was worth the trouble, because new large-scale studies of DNA are causing her and many of her colleagues to rethink the very nature of genes. They no longer conceive of a typical gene as a single chunk of DNA encoding a single protein. “It cannot work that way,” Dr. Prohaska said. There are simply too many exceptions to the conventional rules for genes.

Why Darwin Would Have Loved Botox
Discover, November 2008

Darwin would have loved Botox.

I don’t mean that he would have been first in line at the doctor’s office to get a needle jabbed into his famously furrowed brow. I mean that Darwin would have loved to use Botox as a scientific tool--to eavesdrop on the intimate conversation between the face and brain.

The Evolution of Extraordinary Eyes: The Cases of Flatfishes and Stalk-eyed Flies
Evolution: Education and Outreach, October 2008

The history of life is an unbroken stream of evolution stretching over 3.5 billion years. In order to study it--and in order to describe it--it must be carved into episodes. If scientists want to understand the origin, say, of bats, they do not run experiments to test a hypothesis about how DNA first evolved on the early Earth. They do not do research on the transition from single-celled protozoans to the first animals 600 million years ago. Likewise, they do not get bogged down with bat evolution after bats first evolved--how, for example, bats spread around the world and how they coevolved with their prey. There is only so much time in the day. Science writers follow the same rules to describe evolution. A newspaper article on the evolution of bats must focus only on that brief episode of life’s history. Let its scope grow too large, and it will be too big for a book--or a shelf of books.

This simple necessity can, unfortunately, give people the wrong impression about evolution. We tend to picture evolution as a series of isolated milestones. Once some particular trait evolves, we may assume that evolution simply stops.

The Most Popular Lifestyle on Earth
Conservation Magazine, October-December 2008

Every science has its icon. Genetics has the double helix of DNA. Particle physics has the spiraling tracks of electrons and protons. And if you had to sum up modern ecology in a single picture, it would be the dense mesh of arrows and circles that represents the food web.

The food web’s structure helps ecologists unravel how ecosystems function--whether species go through wild population swings or stay relatively stable. On the Serengeti, for example, acacia trees and grasses form the base of the web, with arrows rising to plant-eaters such as grasshoppers, mice, and gazelle. Each herbivore is in turn eaten by its own set of predators. You don’t have to be an ecologist to recognize the lion’s place in the food web. It’s the king of the jungle, the top predator.

Or is it? Ecologists are beginning to understand that the traditional picture of the food web is missing a vast menagerie of invisible creatures--creatures that might exercise far more control over an ecosystem than even the top predators. Every ecosystem is loaded with tiny parasites--viruses, bacteria, protozoans, fungi, and animals--invisibly feeding on just about every living thing. The Serengeti’s lions, for example, are the sole host to 31 species of worms and flukes, along with two species of bacteria, two arthropods, six protozoans, and ten viruses. In fact, a recent study in Nature found parasites to be so plentiful that, in terms of biomass, they actually outweigh predators in some ecosystems--sometimes by a factor of 20. (1)

Now, for the first time in the history of ecology, a few forward-thinking scientists are pulling parasites out of the shadows and incorporating them into food webs. When they do, the webs then take on a dramatically new look. Parasites are often regarded as a scourge on nature, but--as counterintuitive as it may seem--they may actually keep ecosystems healthy. They may control how top predators coexist with their prey. And when ecosystems begin to suffer, parasites are often the first ones to feel the effects--leading some scientists to believe the tiny creatures could form an early warning system for ecosystems in trouble.

The Search for Intelligence
Scientific American, October 2008

In Robert Plomin’s line of work, patience is essential. Plomin, a behavioral geneticist at the Institute of Psychiatry in London, wants to understand the nature of intelligence. As part of his research, he has been watching thousands of children grow up. Plomin asks the children questions such as “What do water and milk have in common?” and “In what direction does the sun set?” At first he and his colleagues quizzed the children in person or over the telephone. Today many of those children are in their early teens, and they take their tests on the Internet.

In one sense, the research has been a rousing success. The children who take the tests are all twins, and throughout the study identical twins have tended to get scores closer to each other than those of nonidentical twins, who in turn have closer scores than unrelated children. These results--along with similar ones from other studies--make clear to the scientists that genes have an important influence on how children score on intelligence tests.

But Plomin wants to know more. He wants to find the specific genes that are doing the influencing. And now he has a tool for pinpointing genes that he could not have even dreamed of when he began quizzing children. Plomin and his colleagues have been scanning the genes of his subjects with a device called a microarray, a small chip that can recognize half a million distinctive snippets of DNA. The combination of this powerful tool with a huge number of children to study meant that he could detect genes that had only a tiny effect on the variation in scores.

Still, when Plomin and his co-workers unveiled the results of their microarray study--the biggest dragnet for intelligence-linked genes ever undertaken--they were underwhelming. The researchers found only six genetic markers that showed any sign of having an influence on the test scores. When they ran stringent statistical tests to see if the results were flukes, only one gene passed. It accounted for 0.4 percent of the variation in the scores. And to cap it all off, no one knows what the gene does in the body.

“It’s a real drag in some ways,” Plomin says.

Could an Inner Zombie Be Controlling Your Brain?
Discover, October 2008

If you had to sum up the past 40 years of research on the mind, you could do worse than to call it the Rise of the Zombies.

We like to see ourselves as being completely conscious of our thought processes, of how we feel, of the decisions we make and our reasons for making them. When we act, it is our conscious selves doing the acting. But starting in the late 1960s, psychologists and neurologists began to find evidence that our self-aware part is not always in charge. Researchers discovered that we are deeply influenced by perceptions, thoughts, feelings, and desires about which we have no awareness. Their research raised the disturbing possibility that much of what we think and do is thought and done by an unconscious part of the brain--an inner zombie.

Friendly Invaders
The New York Times, September 9, 2008

New Zealand is home to 2,065 native plants found nowhere else on Earth. They range from magnificent towering kauri trees to tiny flowers that form tightly packed mounds called vegetable sheep.

When Europeans began arriving in New Zealand, they brought with them alien plants--crops, garden plants and stowaway weeds. Today, 22,000 non-native plants grow in New Zealand. Most of them can survive only with the loving care of gardeners and farmers. But 2,069 have become naturalized: they have spread out across the islands on their own. There are more naturalized invasive plant species in New Zealand than native species.

It sounds like the makings of an ecological disaster: an epidemic of invasive species that wipes out the delicate native species in its path. But in a paper published in August in The Proceedings of the National Academy of Sciences, Dov Sax, an ecologist at Brown University, and Steven D. Gaines, a marine biologist at the University of California, Santa Barbara, point out that the invasion has not led to a mass extinction of native plants. The number of documented extinctions of native New Zealand plant species is a grand total of three.

How Smart Is the Octopus?

Aristotle didn't have a high opinion of the octopus. "The octopus is a stupid creature," he wrote, "for it will approach a man's hand if it be lowered in the water." Twenty-four centuries later, this "stupid" creature is enjoying a much better reputation. YouTube is loaded with evidence of what some might call octopus intelligence. One does an uncanny impression of a flounder. Another mimics coral before darting away from a pushy camera. A third slips its arms around a jar, unscrews it, and dines on the crab inside. Scientific journals publish research papers on octopus learning, octopus personality, octopus memory. Now the octopus has even made it into the pages of the journal Consciousness and Cognition (along with its fellow cephalopods the squid and the cuttlefish). The title: "Cephalopod consciousness: behavioral evidence."

Gaming Evolves
The New York Times, September 2, 2008

NEW HAVEN--By day, Thomas Near studies the evolution of fish, wading through streams in Kentucky and Mississippi in search of new species. By night, Dr. Near, an assistant professor at Yale, is a heavy-duty gamer, steering tanks or playing football on his computer. This afternoon his two lives have come together.

On his laptop swims a strange fishlike creature, with a jaw that snaps sideways and skin the color of green sea glass. As Dr. Near taps the keyboard, it wiggles and twists its way through a busy virtual ocean. It tries to eat other creatures and turns its quills toward predators that would make it a meal.

Is Dinosaur 'Soft Tissue' Really Slime?
Science, August 1, 2008

In 2005, researchers made headlines when they reported that they had found intact blood vessels from a 68-million-year-old Tyrannosaurus rex. The discovery raised hopes that paleontologists could get their hands on the flesh and blood of vanished animals. This week, however, other scientists challenged the results, arguing that the dinosaur flesh was in fact just coatings of young bacteria. But the original researchers stand by their results, calling the new argument weak. “There really isn’t a lot new here,” says Mary Schweitzer of North Carolina State University in Raleigh.

How Your Brain Can Control Time
Discover, August 2008

Whenever I lose my watch, I take my sweet time to get a new one. I savor the freedom from my compulsion to carve my days into minute-size fragments. But my liberty has its limits. Even if I get rid of the clock strapped to my wrist, I cannot escape the one in my head. The human brain keeps time, from the flicker of milliseconds to the languorous unfurling of hours and days and years. It’s the product of hundreds of millions of years of evolution.

Biodiversity in the Balance
Yale Environment 360, Jun 18, 2008

Last November, the Intergovernmental Panel on Climate Change released its fourth report, a sprawling synthesis of what climate scientists know about global warming. The message was starkly grim--but to appreciate it, you had to spend some time unpacking carefully assembled passages like this:

“There is medium confidence that approximately 20-30% of species assessed so far are likely to be at increased risk of extinction if increases in global average warming exceed 1.5-2.5oC (relative to 1980-1999). As global average temperature increase exceeds about 3.5oC, model projections suggest significant extinctions (40-70% of species assessed) around the globe.”

Translation: While it’s not certain, it’s definitely in the realm of possibility that global warming will put a sizable fraction of the world’s biodiversity at risk of extinction.

What Is A Species?
Scientific American, June 2008

If you visit Algonquin Provincial Park in Ontario, you may hear high, lonesome howls of wolves. You may even be lucky enough to catch a glimpse of a distant pack racing through the forests. But when you show off your blurry pictures back home, what species should you boast that you saw? Depending on the scientist you ask, you may get a different answer. Some may even offer you a few different answers all at once.

Lots of Animals Learn, but Smarter Isn’t Better
The New York Times, May 6, 2008

“Why are humans so smart?” is a question that fascinates scientists. Tadeusz Kawecki, an evolutionary biologist at the University of Fribourg, likes to turn around the question.

“If it’s so great to be smart,” Dr. Kawecki asks, “why have most animals remained dumb?”

Tree of life continues to evolve
The Boston Globe April 28, 2008

Casey Dunn has gathered his share of weird animals. He dredged up sea spiders that live around the docks in Waikiki. He dived to the sea floor to scoop up mud, in search of bizarre, spiny creatures called kinorhynchs that are smaller than a grain of sand.

Dunn, a biologist at Brown University, hunts for weird animals to get his hands on their DNA. Hidden in their genes is a record of the history of the entire animal kingdom, some 700 million years of evolutionary change.

Expressing Our Individuality, the Way E. Coli Do
The New York Times, April 22, 2008

Adapted from Carl Zimmer’s book Microcosm: E. coli and the New Science of Life

We humans differ from one another in too many ways to count. We are shy and bold, freckled and pale, truckers and hairdressers, Buddhists and Presbyterians. We get cancers in the third grade and live for a century. We have fingerprints.

Scientists have only a rough understanding of how this diversity arises. Some of it stems from the different experiences we have, from our time in the womb on through childhood and into our mature years. These molding influences include things like the books we read and the air we breathe. Our diversity also stems from our genes--the millions of typographical differences between one genome and another.

We put a far bigger premium on nature than nurture when it comes to our individuality. That’s one reason why reproductive cloning inspires so much horror. If genes equal identity, then a person carrying someone else’s DNA has no distinct self.

But there’s a deep flaw in this way of thinking, one that blinds us to how biology--human or otherwise--really works. A good counterexample is E. coli, a species of bacteria that lives harmlessly in every person’s gut by the billions. A typical E. coli contains about 4,000 genes (we have about 20,000). Feeding on sugar, the microbe grows till it is ready to split in two. It makes two copies of its genome, almost always managing to produce perfect copies of the original. The single microbe splits in two, and each new E. coli receives one of the identical genomes. These two bacteria are, in other words, clones.

Surely, then, E. coli must be all nature and no nurture. A colony descended from a single E. coli ancestor is just a billion identical cousins, all responding to the world with the same set of genes.

Yet as plausible as this sounds, it’s far from the truth. A colony of genetically identical E. coli is, in fact, a mob of individuals. Under identical conditions, they will behave in different ways. They have fingerprints of their own.

The More We Know About Genes, the Less We Understand Dissection column, April 18, 2008

In life, one mystery gives way, revealing a new one underneath, waiting to be solved.

An early mystery was genes. Scientists did not know what hidden factor lurked inside living things, giving rise to their traits and traveling from parent to child to recreate those traits anew.

The answer, of course, turned out to be DNA: Segments of the molecule encode the proteins and RNA molecules that carry out the work of life, send signals, capture energy and build biomass.

But it quickly became clear that just having genes was not the full secret of life. The genes need to become active at the right time and place. Think about it: Each one of your cells contains genes that can produce hair and toenails, and can crank out neurotransmitters and digestive enzymes. If all your genes did churn away, your body would become a hideous, useless jumble. Our life depends on the courteous restraint of our genes.

Your Brain Is a Mess, but It Knows How to Make Fixes Dissection column, April 4, 2008

It’s easy to be over-dazzled by the brain. Who could be unimpressed by the billions of neurons packed into our skulls, linked together by trillions of connections, capable of encoding memories from decades ago, of playing a saxophone, of sending space probes out of our solar system? We naturally want to know how our brain got to be so good. But there’s an even more interesting question worth asking: How do we manage to survive with a brain that’s so bad?

Distinguishing Artificial From Natural Is Possible, for Now Dissection column, March 21, 2008

We like to tell ourselves that it's easy to distinguish between the natural and the artificial, but they have a knack for fooling us. When European colonists traveled through the patchwork of forests and meadows of New England, they thought they were exploring primeval nature. In fact, Native Americans had been tending it carefully with fires for centuries. When the Viking probe snapped a fuzzy picture of a mountain on Mars in 1976, some people were sure it showed a giant face carved by Martians. When another probe took a sharper picture in 2001, all trace of the face had vanished.

Today the mystery of the natural versus the artificial is moving from mountains and forests down to the microscopic realm. Scientists can now synthesize DNA from scratch. They regularly add new genes to bacteria, plants and animals. They are learning how to manufacture whole genomes. Can we tell the difference between our growing menageries of engineered organisms and natural ones? A fascinating new study from scientists at Lawrence Livermore National Lab in California shows that we can -- at least for now.

Spinach, Lettuce, and the Limits of Bioterrorism
Slate, March 19, 2008

Listen to my article on Slate's podcast (mp3 file here)

An outbreak of E. coli isn't usually the stuff of feel-good stories. Feel-bad is more like it--or even feel-organ-failure. But recent E. coli outbreaks can offer us a bit of solace. We live in the anxious age of synthetic biology, when scientists can reconstruct entire genomes from raw chemicals, and when we all fret that someone is going to use this new technology to create a monster bug and unleash a man-made plague. According to one government report, "The effects of some of these engineered biological agents could be worse than any disease known to man." But a close look at recent outbreaks of E. coli--and a closer look at the bacteria themselves--may help us to put aside our fears for the moment. Engineering plagues is harder than it looks.

How to Date the Grand Canyon: Go With the Flow
Dissection column,, March 6, 2008

The Grand Canyon is a victim of terrible press.

Its banded walls make up one of the most magnificent landscapes on Earth. And yet it seems the only time reporters bother to mention its geology is when they are writing about creationists and their bogus claims that the Grand Canyon formed a few thousand years ago. It's a shame, because the real story of the Grand Canyon is a riveting epic. Even its scientific history is fascinating: Figuring out just how old the Grand Canyon is has challenged geologists for 150 years. And just this week, the mystery may be solved.

Social, and Smart
The New York Times, March 4, 2008

For the past two decades, Kay E. Holekamp has been chronicling the lives of spotted hyenas on the savannas of southern Kenya. She has watched cubs emerge from their dens and take their place in the hyena hierarchy; she has seen alliances form and collapse. She has observed clan wars, in which dozens of hyenas have joined together to defend their hunting grounds against invaders.

“It’s like following a soap opera,” said Dr. Holekamp, a professor at Michigan State University.

Throughout her career, Dr. Holekamp has remained vigilant against anthropocentrism. She does not think of the hyenas as long-eared people running around on all fours. But the lives of spotted hyenas, she has concluded, share some profound similarities with our own. In both species, a complex social world has driven the evolution of a big, complex brain.

The Encyclopedia of Life, No Bookshelf Required
The New York Times, February 26, 2008


Imagine the Book of All Species: a single volume made up of one-page descriptions of every species known to science. On one page is the blue-footed booby. On another, the Douglas fir. Another, the oyster mushroom. If you owned the Book of All Species, you would need quite a bookshelf to hold it. Just to cover the 1.8 million known species, the book would have to be more than 300 feet long. And you’d have to be ready to expand the bookshelf strikingly, because scientists estimate there are 10 times more species waiting to be discovered.

It sounds surreal, and yet scientists are writing the Book of All Species. Or to be more precise, they are building a Web site called the Encyclopedia of Life ( On Thursday its authors, an international team of scientists, will introduce the first 30,000 pages, and within a decade, they predict, they will have the other 1.77 million.

Honey Bees Give Clues on Virus Spread
“Dissection” column,, 2/22/08


Everyone likes a medical mystery -- even more so when the mystery in question is solved. When a few people in Queens developed fevers in 1999, scientists pinpointed an American strain of West Nile virus. When people in East Asia began to get particularly wicked coughs in 2003, scientists discovered an entirely new virus called SARS. As much as we admire the ingenuity that went into solving these medical enigmas, that doesn't mean we should ignore the medical-sleuthing stories that haven't yet reached a satisfying ending. Their very mystery actually says something important about how nature works.

Revealed: Secrets of the Camouflage Masters
The New York Times, February 19, 2008


WOODS HOLE, Mass. --The cuttlefish in Roger Hanlon’s laboratory were in fine form. Their skin was taking on new colors and patterns faster than the digital signs in Times Square.

The Natural History of the Only Child
“Dissection” column,, 2/8/08

Modern life means small families. Starting about two centuries ago, families in Western Europe began to shrink, and then -- country by country, continent by continent -- the rest of the world followed suit. The trend is so big that it may rein in the world population's exponential growth, perhaps even causing it to stop growing altogether over the next century.

But exactly why families are shrinking is a mystery. Rising living standards seem to have something to do with it. It's certainly true that as living standards rose in England -- as children died less from diseases, as the country overall became richer -- the size of the English family shrank. When other countries became wealthier, their families shrank, too. These days, affluent countries tend as a rule to have smaller families than poor ones.

Artificial Life? Old News

Dissection: Commentary at, January 25, 2008

Yesterday the news broke, and it broke big: genome pioneer Craig Venter and his team of scientists at his eponymous institute had created a microbe’s genome from scratch. Massive stories ran in newspapers and magazines, tingling with the sense that we were on the edge of a revolution. Time’s piece was accompanied by a foreboding picture of Venter in a forest, wearing a dark coat and scarf, his beard giving his scowl a particularly dire look. The picture matched the story’s ominous mood: “He has gone beyond merely sequencing a genome and has designed and built one. In other words, he may have created life,” the article intoned. The Economist promised that when Venter is done, he will “have erased one of the last mythic distinctions in science--that between living and non-living matter.”

I get the impression I am supposed to be tingling, my heart racing with exaltation or terror or...something. And yet I feel like I have a lesion in my amygdala, unable to respond to the threat of an electric shock. In some ways, this is actually old news. And in other ways, it’s news that hasn’t yet been written, and won’t be for decades.

Isolated Tribe Gives Clues to the Origins of Syphilis
Science, January 18, 2008

In 1494, King Charles VIII of France invaded Italy. Within months, his army collapsed and fled. It was routed not by the Italian army but by a microbe. A mysterious new disease spread through sex killed many of Charles's soldiers and left survivors weak and disfigured. French soldiers spread the disease across much of Europe, and then it moved into Africa and Asia. Many called it the French disease. The French called it the Italian disease. Arabs called it the Christian disease. Today, it is called syphilis.

The sensational debut of syphilis inspired centuries of debate. Some have argued that Columbus's crew brought the disease from the New World to Europe; others say the disease existed unrecognized for centuries in the Old World before turning virulent. This week in the journal PLoS Neglected Tropical Diseases, a team of researchers argues that neither hypothesis is correct. Syphilis originated as a milder, nonsexual disease in the New World, they say, and it evolved into its current form after Europeans arrived. Among the evidence they offer is a mysterious disease restricted to an isolated tribe in a South American jungle. Its DNA, they argue, reveals that it is a kind of protosyphilis.

Twenty-first-century anatomy lesson
Nature, January 17, 2008

A review of Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body by Neil Shubin

Six hundred years ago, anatomists were rock stars. Their lessons filled open-air amphitheatres, where the curious public rubbed shoulders with medical students. While a surgeon sliced open a cadaver, the anatomist, seated above on a lofty chair, deciphered the exposed mysteries of the bones, muscles and organs.

Modern anatomists have retreated from the stage to windowless medical-school labs. They have ceded their public role to geneticists unveiling secrets encrypted in our DNA. Yet anatomists may be poised for a comeback, judging from Your Inner Fish. Neil Shubin, a biologist and palaeontologist at the University of Chicago, Illinois, delves into human gristle, interpreting the scars of billions of years of evolution that we carry inside our bodies.

Romance Is An Illusion
Time, January 17, 2008

There's nothing like being in love. Minutes seem to creep and fly at the same time. We get lost on the way home, thinking of the next date. Music cries out to us alone, and the full moon winks our way. Long after other memories fade, the recollection of love lingers. It's pure magic. Or at least that's what we like to tell ourselves.

The Sixth Extinction
Il Sole 24 (Italy), January 13, 2008

Last fall, the organizers of the Rome Science Festival asked me to come give a lecture about mass extinctions--about how our planet has experienced huge die-offs in the past, and whether it may be on the verge of another die-off today. Only after I began to prepare my talk did I realize how fitting it was to speak of such matters in Italy. For it is in Italy that some of the most important advances in understanding extinctions have taken place.

Migration, Interrupted: Natureís Rhythms at Risk
The New York Times, January 1, 2008


A review of No Way Home: The Decline of the World's Great Animal Migrations, by David S. Wilcove.

The world is etched with invisible paths, the routes taken each year by uncountable swarms of geese, elk and salmon, of dragonflies, zebras and leatherback turtles.

Their migrations speak to us in some unfathomably deep way. Birders flock to stopover sites like Cape May, N.J., to watch birds on their journeys to the far north in the spring and back to the tropics in the fall. Eco-tourists head for the Serengeti to train binoculars on herds of wildebeest that stretch to the horizon. American schoolchildren watch monarch butterflies hatch from chrysalises in their classrooms and then see them off on their trip to Mexico.

But in his new book “No Way Home,” David Wilcove, a Princeton biologist, warns that “the phenomenon of migration is disappearing around the world.”

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